Blood Pressure Flashcards
Where is maximum BP?
Aorta during systolic ejection
When is minimum aortic blood pressure?
During isovolumetric contraction - diastole
What is blood pressure a function of?
Stroke volume and arterial compliance
What is the trend of arterial compliance over a life time?
Compliance decreases as age increases
What are physiological values for blood pressure at ages:
1) Up to 45 years
2) 45-60 years
3) above 60 years
1) Up to 45 years
Diastolic = 60-90mmHg
Systolic = 100-140mmHg
2) 45-60 years
Systolic = 150mmHg
3) 60+ years
Systolic = 160mmHg
What is hypotension and its results?
Low blood pressure
Degradation of tissues
What is hypertension and its results?
High blood pressure and damaged vessels
What is the trend of blood pressure values from the aorta to the right atrium?
Mean blood pressure falls as it leaves the aorta to the arteries, but the pressure is higher in the greater arteries due to less compliance.
What is compliance?
The tendency of the arteries and veins to stretch in response to pressure has a large effect on perfusion and blood pressure.
Veins have a much higher compliance than arteries (largely due to their thinner walls).
What is the systemic circulation?
Greater circulation.
From left ventricle to the peripheral capillaries via the arteries.
Returns to the right atrium via the veins.
What is the pulmonary circulation?
Lesser circulation.
From right ventricle to the lungs.
Returns to the left atrium.
Explain the total blood volume.
4-5L
80% of this is in the veins, right heart and pulmonary vessels.
This is the low pressure system.
This is the blood reservoir and can be released by vasoconstriction is necessary.
What is the central venous pressure (CVP)?
Normally 4-12mmH2O.
Measured by the right atrium.
A good indicator of blood volume.
If the blood volume increases (transfusion) 99% of the blood goes to the low pressure system.
If the blood volume decreases, this will be a decrease almost entirely in the low pressure system.
Explain the cardiac output (CO).
5.6L/minute at rest.
CO = Heart Rate * Stroke Volume
With an increase of HR the output can be increased to 15-20L/minute.
Stroke Volume = volume of blood ejected from ventricles during systole = 0.08L
Heart Rate = During rest = 70bpm
What is the average oxygen consumption at rest?
250mL/minute
Explain the flow resistance.
What are its values in the right and left ventricles?
The flow resistance is much lower in the pulmonary circulation than in the systemic.
Depends greatly on the radius of the tube (r^4).
The lesser arteries and arterioles account for 50% of the total peripheral resistance.
Right ventricle = 15mmHg (2kPa)
Left ventricle = 100mmHg (13kPa)
What is the equation from blood pressure?
P = Q * R P = blood pressure Q = blood flow R = resistance of vessels
Explain how arteries convert the alternating flow of the contracting heart to a steady flow in the vessels.
The greater arteries convert the alternating flow of the heart to a steady flow though the arteries.
This is possible due to their great compliance (elasticity).
The blood is ‘stored’ in the artery’s dilated lumen when the heart contracts, therefore offsetting the change in BP.
When the aortic valves close the arteries constrict.
The end result is an almost steady flow.
Explain how a false reading can be gained from a blood pressure measurement.
If readying multiple times in a row without rest, the diastolic pressure will be elevated due to blood pooling.
If the cuff is too loose or too tight, this will give a false reading.
Explain the palpation method of taking blood pressure.
Minimum systole value can roughly be measured without any equipment.
Used for emergency situations.
Radial artery gives a minimum of 80mmHg.
This method is not accurate.
With the use of a sphygmomanometer a more exact systolic value can be obtained.
Diastolic pressure cannot be measured in this way.
Explain the auscultatory method of taking blood pressure.
Stethoscope and sphygmomanometer are used.
Gives absolute results.
Measured externally at the level of the heart using the brachial artery.
The first sound heard (Korotkoff sound) indicates systolic pressure.
When the sounds stop, this indicates diastolic pressure.
Explain the oscillometric method of taking blood pressure.
Functionally similar to the auscultatory method.
An electronic pressure sensor is used.
Can be used at home, or by untrained staff.
But does NOT give exact values.
